1. Field of the Invention
The present invention relates to a communication system where a single subscriber line terminal (SLT) unit on a network side and a plurality of terminal units on a user side share a single transmission line and transfers information by time division multiplexing through polling.
As a typical example of such a type of communication system, there is an asynchronous transfer mode-passive optical network (ATM-PON) communication system. The present invention will be explained below with reference to the example of this ATM-PON communication system. In particular, the present invention provides an improved technique for dynamic bandwidth allocation for handling variable rate traffic in such an ATM-PON communication system.
2. Description of the Related Art
As will be explained in detail later with reference to the drawings, in a conventional communication system handling variable rate traffic, no consideration at all is given to parameters such as the peak cell rate (PCR), sustainable cell rate (SCR), and burst tolerance (BT). Therefore, the problem arose of allocating large bandwidths continuously without limit to virtual connections (VC) in which large numbers of cells are accumulated in buffers of the terminal units on the user side. Therefore, the subscriber line terminal (SLT) unit at the network side could no longer make effective use of the communication resources as planned.